Remove the ability in dart2js to turn off syntax-only generic methods.

pkg/compiler/lib/src/dart2js.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.cmdline;
 
 import 'dart:async' show EventSink, Future;
 import 'dart:convert' show UTF8, LineSplitter;
 import 'dart:io' show exit, File, FileMode, Platform, stdin, stderr;
 
@@ skipping 120 matching lines @@
   bool showWarnings;
   bool showHints;
   bool enableColors;
   // List of provided options that imply that output is expected.
   List<String> optionsImplyCompilation = <String>[];
   bool hasDisallowUnsafeEval = false;
   Map<String, dynamic> environment = new Map<String, dynamic>();
 
   void passThrough(String argument) => options.add(argument);
 
+  void ignoreOption(String argument) {}
+
   if (BUILD_ID != null) {
     passThrough("--build-id=$BUILD_ID");
   }
 
   void setLibraryRoot(String argument) {
     libraryRoot = currentDirectory.resolve(extractPath(argument));
   }
 
   void setPackageRoot(String argument) {
     packageRoot = currentDirectory.resolve(extractPath(argument));
@@ skipping 174 matching lines @@
         '--output-type=dart|--output-type=dart-multi|--output-type=js',
         setOutputType),
     new OptionHandler(Flags.useKernel, passThrough),
     new OptionHandler(Flags.noFrequencyBasedMinification, passThrough),
     new OptionHandler(Flags.verbose, setVerbose),
     new OptionHandler(Flags.version, (_) => wantVersion = true),
     new OptionHandler('--library-root=.+', setLibraryRoot),
     new OptionHandler('--out=.+|-o.*', setOutput, multipleArguments: true),
     new OptionHandler(Flags.allowMockCompilation, passThrough),
     new OptionHandler(Flags.fastStartup, passThrough),
-    new OptionHandler(Flags.genericMethodSyntax, passThrough),
+    new OptionHandler(Flags.genericMethodSyntax, ignoreOption),
     new OptionHandler(Flags.initializingFormalAccess, passThrough),
     new OptionHandler('${Flags.minify}|-m', implyCompilation),
     new OptionHandler(Flags.preserveUris, passThrough),
     new OptionHandler('--force-strip=.*', setStrip),
     new OptionHandler(Flags.disableDiagnosticColors, (_) {
       enableColors = false;
     }),
     new OptionHandler(Flags.enableDiagnosticColors, (_) {
       enableColors = true;
     }),
@@ skipping 685 matching lines @@
   @override
   void close() {
     // Do nothing.
   }
 
   @override
   void addError(errorEvent, [StackTrace stackTrace]) {
     // Ignore
   }
 }